1. Field of the Invention
The present invention relates to a satellite communication data delivery method for performing data delivery from a master station by way of a plurality of slave stations via a satellite, and a slave station and a master station used for the method.
2. Description of the Related Art
Conventionally, communication technologies utilizing satellites have been implemented in satellite broadcasting systems such as so-called BS broadcasts and CS broadcasts and the SNG (Satellite News Gathering) system wherein information from information stations deployed at multiple points is transmitted to the main station, or data delivery systems wherein images or data is delivered in a specific group. One characteristic of the listed satellite communication is that the communication is satellite communication wherein information is transmitted/received between one master station and a plurality of slave stations. For such point-to-multipoint satellite communication, the first concern is how to assign and use the frequency band of communication waves occupied by the system.
FIG. 9 shows a schematic diagram of frequency assignment in a point-to-multipoint satellite communication data delivery system according to the related art. In FIG. 9, 1 represents a large-capacity channel having a wide bandwidth, and 2 a small-capacity channel having a narrow bandwidth. The large-capacity channel 1 is a data delivery channel for transmitting images, voice and data from a master station to slave stations. By extending the bandwidth of the data delivery channel, transmission capacity and transmission rate of information sent from a master station to slave stations are enhanced. The small-capacity channel 2 is provided as many as the number of slave stations N as shown in FIG. 9, and assigned to each slave station. The slave stations transmit response data to the master station over the small-capacity channel 2.
Since the frequency resource is limited, one communication system is typically operated within a frequency band exclusively assigned to the system. Thus, once the bandwidth of the large-capacity channel 1 and the bandwidth of the small-capacity channel 2 are determined, the number of the small-capacity channel 2, that is, the number of slave stations accommodated in the system is determined. To increase the number of slave stations, the bandwidth of the small-capacity channel 2 is made narrower. However, it is necessary to set the minimum bandwidth depending on the performance of communication apparatus used for transmission/reception. Thus the number of the slave stations cannot be increased in excess of a certain number. Even in case the frequency band occupied by a communication system is extended to increase the number of small-capacity channel 2, that is, the number of slave stations, the scale of the receiving system in the master station or repeaters on satellites is inevitably enlarged.